The present invention relates in general to a method of forming an array of underground support columns. More specifically, a preferred embodiment of the present invention relates to a method for forming an interconnected underground, impermeable wall. A second embodiment of the invention provides a method for treating and stabilizing highly toxic underground plumes to reduce or eliminate migration of the toxic plumes. The present method may be utilized in caving soils and is performed without causing the settlement of adjacent soil structure. The present invention avoids settlement of adjacent soil structure by maintaining a positive hydrostatic head in each hole as the hole is being formed.
The prior art includes U.S. Pat. No. 3,969,902 to Ichise et al and teaches a method for constructing a continuous row of underground piles. The single greatest drawback of Ichise et al is that the method will simply not work in caving soils. Ichise et al proposes that the hole is drilled first. Ichise teaches at column 3, lines 32-35, lines 50-53 and lines 60-63, that a hole is completely dug before any ground hardening liquid is inserted through inner tube 6. The difficulty with the Ichise et al approach is that, if it is attempted in caving soils, the caving side walls will effectively prevent the formation of a cylindrical hole and, alternately, ground water may enter the hole and seriously weaken the underground structure. A second drawback of Ichise et al is that the auger used requires a dual injection system which in turn requires the use of a complex double walled earth drill capable of simultaneously injecting a ground hardening liquid and mortar (see column 1, lines 60-64 and column 3, lines 36-43).
It is also known in the prior art to utilize a drilling system wherein a high pressure jet is provided near the cutting tip of the auger to hydraulically assist the breaking up of soil and to inject cement slurry (or other slurry) to create a soil cement mixture (or other mixtures) which forms an underground column. Those prior art patents include three patents owned by the assignee of the present application. Those patents include U.S. Pat. Nos. 4,793,740; 4,958,962 and 5,396,964. Those three patents are hereby incorporated herein by reference as if set forth in full. Those patents teach the combined mechanical and hydraulic cutting and mixing as a hole is being formed. Those patents teach the use of a positive hydrostatic head in the hole relative to adjacent soil. However, those patents do not teach a method of extending the diameter of a hole by the use of a high pressure, high velocity slurry pumped through a nozzle mounted near the outer diameter of the hole, whereby the diameter of the hole is effectively being expanded while the hole is being formed and while a positive hydrostatic head is being maintained in the hole relative to the adjacent soil.
The present invention provides a method of forming an interconnected underground structure, such as an impermeable wall or a support footing for buildings or structures, without causing settlement of adjacent soil structure and which can be used in caving soils.
It is, therefore, a primary object of the present invention to provide a method capable of forming an interconnected underground structure which can be utilized in caving soils and which does not cause settling of adjacent soil.
A further object of the present invention is to form an interconnected underground wall wherein a positive hydrostatic head is maintained during the entire time frame in which each hole is being formed, relative to the adjacent soil.
Yet another object of the invention is to provide a method of forming an impermeable underground wall which effectively prevents the lateral migration therethrough of underground water as well as underground water borne toxic materials.
A further object of the invention is to provide a method capable of solidifying underground soil and forming an impermeable underground structure of a soil cement mixture which is both impermeable and which is resistant to the lateral flow of underground toxic materials.
Yet another object of the invention is to provide a method of surrounding a toxic underground plume with a wall and thereafter modifying the entire volume contained by the wall to reduce or prevent the migration of the toxic plume.
Other objects and advantages of the invention will become apparent from the following description and the drawings wherein: